I worked with many types of tubing and work in many labs in school.
The preffered tubing material is by far tygon over any vinyl based tubing. It comes down to chemical resistance, memory , halflife , flexibility, operating temperature , and strenght. Tygon out performs any vinyl based tubing (ie. clearflex) without a doubt.
But because most of the overclockers today that watercool dont exactly have a huge budget to spend on tubing - many turn to clearflex. To an untrained eye the clearflex seems just as good as tygon, and thats okay since you will probably never come to a point were tygons advantages will favor it.
(execpt flexibility and temp resistance - most common grades of tygon can withstand boiling liquids passing through it .....so if your fan on your radiator ever fails melted tubing will not be a problem.)
I use tygon and will never go back to silicone or vinyl.........I am fortunate enough to have the extra $$$ for tygon (have a 50ft. roll at home

) and believe you shouldn't be cheap when it comes to playin with eletrical components and water.
But if your in high school or just a bit of a cheapskate then buying tygon doesnt benefit you at all. (kinda like why buy a porshce if you can have 4 fords)
Hope this helps some of you guys in choosing the right tubing.